I went from LaunchBar to Quicksilver to Spotlight to LaunchBar. Can't live without that clipboard history! I don't use many of its other features anymore though.

Preview annotates things well enough that I never use Skitch, although Skitch is cool if you want to use the sharing features.

You might be missing out on Dropbox. I wouldn't want to go without it these days as I use more than one computer regularly and don't have to remember to commit 'WIP' on a branch before I head home, I just drop the mic and get the fuck out. YMMV.

Divvy is great. I use it w/ SizeUp every day and wouldn't want to go without them. I don't miss xmonad at all anymore.

Other than that I install 1Password, The Unarchiver, Growl, CrashPlan, Flux, TextMate, iTerm, and GitX and I am good to go.

I seem to shed tools as OS X improves as well, but I hope that nobody is using plan9 in 40 years! ;-)